This invention relates generally to hydraulic systems and more particularly to an automated control for adjusting the displacement of a variable displacement hydraulic motor, especially for use in aircraft actuation systems.
Variable displacement hydraulic motors find great utility in systems and application where the load requirement placed upon the motor may vary widely. In such event, substantial savings in pressurized motive flow can be achieved by minimizing motor displacement so that power required therefrom is relatively low. More specifically, in such instance it is conventional to reduce motor displacement when power load requirements are low in order to minimize the power utilized in the hydraulic actuation system.
In aircraft environment applications, economy of components, and simplicity of systems become paramount in order to minimize weight and size requirements. Another factor which must be considered during the operation cycle of such a hydraulic actuation system is the imposition of large aiding loads wherein the load is being driven in a particular direction as fast or faster than that dictated by the hydraulic control system. In such instance the hydraulic motor actually operates in a braking mode tending to resist the over running load.
A typical hydraulic control system of the type referred may utilize a speed sensor in order to control the hydraulic motor to operate at a preselected, desired speed. Particularly, such system would include an electronic sensor to sense motor output rotational speed, an electronic processing control system for analyzing the speed signal, comparing it to a desired speed signal and then generating a suitable electrical output signal that is applied to an electrohydraulic element, such as a servo valve, for operating a servo actuator to adjust motor displacement in order to maintain the desired motor speed. Such a system is typical and is characterized by a plurality of various components and elements in order to provide a control system of efficient operation.